Load size and energy delivery in birds feeding nestlings: Constraints on and alternative strategies to energy-maximization.

The Orians-Pearson model of central place foraging for multiple-prey loaders assumes, as does most of current foraging theory, (i) that the quantity to be maximized is rate of energy delivery, and (ii) that the capacity of the foraging animal is the only relevant constraint on this rate. When applied to the case of birds feeding nestlings the model predicts, therefore, that the parents should select whichever load size maximizes the rate of energy delivery to the young.We assume here (i) that the parents could alternatively maximize the rate of energy delivery to the nest (m-strategy), maximize the time available for activities other than foraging (e.g. brooding) (b-strategy), or minimize the frequency of visits to the nest (v-strategy). We further assume (ii) that the nestlings impose constraints on the foraging behaviour of their parents in that there is a maximum load size that a brood can receive, as well as a maximum and a minimum rate of energy delivery that is acceptable. These three quantities are increasing functions of the age of the nestlings.Load size as a function of the age of the nestlings is predicted to increase initially and then to approach either the load size corresponding to maximum parental efficiency (m- and b-strategies) or a larger load size (v-strategy). For the b- and v-strategies rate of energy delivery is predicted to correspond to the minimum requirement of the nestlings throughout the nestling period. For the m-strategy energy delivery is predicted to be the maximum energy requirements of the nestlings initially, and then to level off to the energy delivery rate that corresponds to the maximum parental efficiency. As these strategies are not always compatible, foraging behaviour in a particular case may be an adaptive compromise between them.

Why do males emerge before females? protandry as a mating strategy in male and female butterflies.

The reproductive strategy of butterfly males can be defined as being to maximize the number of females mated. We have earlier shown that, if the eclosion period of females is regarded as given, males should emerge before females to achieve maximal reproductive success. However, females may also be considered to have a reproductive strategy with respect to the issue "when to emerge". In this paper we assume that females are selected to minimize the time spent unmated (to minimize prereproductive death), and analyze when females should optimally emerge in relation to males to achieve this end. We show that there is no conflict between the sexes with respect to the timing of eclosion when the length of the eclosion period is approximately equal for males and females. Thus, protandry should be considered a reproductive strategy of both males and females.

Why do males emerge before females? : A hypothesis to explain the incidence of protandry in butterflies.

In butterflies and many other insects there is a general tendency for males to emerge before females. This is known as protandry. In this paper we advance the hypothesis that protandry is a reproductive strategy of males, resulting from competition for mates, and should primarily occur in species maintaining female monogamy. Our hypothesis is corroborated by applying a mathematical treatment to a theoretical population with seven defined properties, all of which are argued to be reasonable assumptions for natural populations.